1. Field of the Invention
The invention relates to a method and apparatus for winding lengths of flexible material such as wire, rayon filaments, glass filaments, yarn, thread, rope, ribbon, tape, slit plastic sheeting, cable and the like on mandrels, and to methods of packaging such windings; to the packages produced by such method and apparatus; and to endforms forming part of the mandrels on which such windings are formed. More specifically, the invention relates to the winding and forming of any bendable, filamentous or ribbon-like substance, including all crosssectional shapes of wire or other substance and especially to materials with slippery surfaces, unusual stretch characteristics, or which require minimum surface pressure and/or minimum stretching either while being wound or subsequent to winding, in packaged form.
2. Prior Art
This invention is an improvement over that disclosed in U.S. Pat. No. 3,178,130, assigned to the Assignee of the subject application. The method, apparatus and packages formed by the invention of that patent are limited by the package diameters specified therein. Limitations on the package diameters were previously considered necessary because the endforms of the mandrels on which the packages were wound were designed using graphical techniques to generate the circular curve form of the endform from a center point or points lying outside of the finished package. Such a graphical and geometrical technique for generating the circular curves of the endforms causes limitations on the upper limit of the package diameters because at some point the curves of the endforms (being circular) begin to come back on themselves.
Another problem resulting from the techniques disclosed in the aforementioned U.S. patent is that the circular curves are only approximations to the exact paths that a wind builds out to as the diameter of the wind changes. If the geometrical configuration of the endforms is not correct, the ends of the wind build up causing inward slip into the valley of the wind as the wind builds on the winding core. Such inward slip eventually obscures the payout hole which is formed as a radial opening in the side of the winding extending from the exterior of the winding to the inner axial space thereof. Because in such windings formed with a radial hole, it is desirable to pay out the material from the inside of the winding through the radial opening in the payout hole, the obstruction caused by any winds in the payout hole may cause possible twist problems because the winding, as it is paid out through the radial opening, becomes entangled with the windings obscuring the payout hole.
Moreover, the obscuring of the payout hole by the slippage of the winding may present difficulty in locating the payout hole. An incorrect payout hole location will result in the material encountering a winding within the payout hole, which generally hinders paying out of the material through it.
Moreover, if the endforms of the mandrel on which the material is being wound are too wide at any point for the winding conditions, the material being wound (especially at high winding speeds) will "fall off" to a diameter which is less than that which it should be, thus causing possible tangles as the material is paid out through the payout hole formed by the radial opening in the side of the winding.
Also, if material slips to a diameter less than it should be, compression would be impossible without damaging the material, and package repeatability would be lost. A loop at a diameter less than it should be must become longer because during compression the coil diameter increases slightly.
The aforementioned U.S. patent describes a design method for quick turnaround angles of the wind as it is being wound on the mandrel allowing for straight line and circular approximations. In present-day winding apparatus, different cams are available with various turnaround angles. However, with the techniques as described in the aforementioned U.S. patent, as the turnaround angles of the cams become longer (ultimately attaining a sinusoidal path) the approximations in the geometrical approach for forming endforms results in an increasing error such that the results of using the design method disclosed in the aforementioned patent produce useless and unstable winds, in addition to the aforementioned problem of limiting the diameter of the wind.